A Study on the Antimicrobial Activity of Algae Extract: The Fucales Order Case ^†

Abstract

Over the years, foodborne pathogens have caused countess health problems and massive financial losses. Therefore, an essential goal for the food industry is to prevent food contamination and the related foodborne illnesses as microbial contamination of food items during their acquiring and distribution processes is still a hygienic issue. Moreover, there is an important movement leading to the pursuit of more natural and safe food supplies and ingredients with a special emphasis on the vegan and vegetarian community; as a result, there has been a resurgence in demand for natural and eco-friendly products as a replacement for synthetic ingredients. In this context, and due to their active substances, macroalgae stand out as they are known for possessing antibacterial qualities among other abilities. Because of this, the current study updates our understanding of microbial pollutants in the food industry and compiles the latest updates on the scientific reports on antimicrobial activity of the edible brown algae species with special attention to the algae Bifurcaria bifurcata, Fucus spiralis, and Ascophyllum nodosum. These species which belong to the Phaeophyceae class and order Fucales are reportedly rich in active compounds and are still an undervalued resource. So, the ability of algal extracts to stop the growth of various significant food pathogens is reviewed herein, while considering their advantageous effects on food safety and quality issues.

1. Introduction

Rich in biodiversity, the oceans have gained global importance and are increasingly under scrutiny as a source of natural products. Among the many organisms living in marine habitats, macroalgae have attracted much interest due to their diversity and potent bioactive metabolites [1]. Members of the Fucales family, a particular group of brown macroalgae, are known for their ecological importance, metabolite composition, and potent bioactive properties.

These metabolites, ranging from polysaccharides [2] to phenolic compounds [3] and terpenoids [4], not only contribute to the ecological interactions of the algae but also possess promising bioactive properties. This work focuses on exploring the antimicrobial potential of extracts from macroalgae belonging to the Fucales family, namely Bifurcaria bifurcata, Fucus spiralis, and Ascophyllum nodosum. Figure 1 presents photographs of this species in detail and in their natural environment. The study aims to elucidate the spectrum of antimicrobial activity of these extracts against a range of significant microorganisms, highlighting food-related pathogens.

2. Discussion

With the aim of evaluating the latest published developments in the field of antimicrobial capacity of algal extracts, available databases were searched using the name of the alga and antimicrobial activity as keywords. A summary of the main results published in the last five years is presented in Table 1.

Several important foodborne microorganisms can cause various diseases when ingested through contaminated food. Some of the most important of these are: Salmonella, Escherichia coli, Listeria monocytogenes, and Staphylococcus aureus [5]. Macroalgal extracts could play a role as inhibitors of these pathogens [6,7]. For example, the pathogenic effect of toxins produced by E. coli is one of the most important causes of foodborne illness worldwide [7,8]. Moreover, there are studies also supporting the inclusion of alga extracts as food preserves [9,10].

The antimicrobial activity of B. bifurcaria extracts obtained by maceration with solvents of different polarity has been studied previously. The results highlighted the potential of B. bifurcaria as an effective antimicrobial agent, as all extracts were active against five of the six microorganisms tested [11]. In another work, the algal extract (hexane–isopropanol–water (10:80:10)) was tested against Bacillus cereus, Bacillus subtilis, Geobacillus stearothermophilus, L. monocytogenes, S. aureus, and Staphylococcus haemolyticus. The results showed antimicrobial activity against all microorganisms, with seasonal variation in activity and minimum inhibitory concentrations ranging from 0.3 mg/mL (G. stearothermophilus) to 19.9 mg/mL (S. aureus) [12]. In addition, the water extracts of B. bifurcaria were found to have potent antifungal activity against Penicillium digitatum, Penicillium expansum, and Penicillium italicum [13].

Table 1. Selected studies on the antimicrobial activity of Bifurcaria bifurcata, Fucus spiralis, and Ascophyllum nodosum.

Extraction Technique	Microorganism Tested	Major Results	Ref.
Bifurcaria bifurcata
Sequential extraction (RT); (Hx, MeOH, Wt) 1:20 (m/v)	Epidermophyton floccosum, Microsporum canis, Microsporum gypseum, Trichophyton mentagrophytes var. interdigitale; Thrichophyton rubrum, Trichophyton verrucosum.	MeOH extracts demonstrated antifungal capacity against human dermatophyte fungi; the antifungal activity seems to be seasonally/geographically influenced	[14]
Maceration 50 °C, 24 h EtOH, AcO, EtAc, Chl and Hx	Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Pseudomonas aeruginosa, Salmonella enteritidis, Escherichia coli	Strong inhibition activity; all extracts were active against all microorganisms except E. coli	[11]
Maceration RT 60 min Hx–IPr-W (10:80:10)	Bacillus cereus; Bacillus subtilis; Geobacillus stearothermophilus; Listeria monocytogenes; Staphylococcus aureus; Staphylococcus haemolyticus;	MICs values between 0.9 mg/mL (B. cereus) and >19.9 (L. monocytogenes) spatial and seasonal variations; inconsistencies between disc diffusion and broth dilution methods	[12]
Maceration RT, 4 days MeOH	Penicillium digitatum, Botrytis cinerea	Active against both microorganisms in the four harvest seasons tested	[15]
Maceration 48 h, RT, +30 min. ultrasonication	Penicillium digitatum, Penicillium expansum, Penicillium italicum	Strong antifungal activity; effective in reducing the mycelial growth.	[13]
maceration RT 48 h methanol (90%)	E. coli, Staphylococcus aureus, Bacillo subtilis, P. aeruginosa	MICs from 0.11 to 1.87 mg/mL	[13]
Sequential extraction MeOH; DCM/MeOH (50:50), DCM	Escherichia coli, Proteus mirabilis, Staphylococcus aureus CECT 976, Staphylococcus aureus ATCC 25923	MIC of 0.02 µg/mL against P. mirabilis, 0.3 µg/mL against S. aureus CECT 976 and 1.8 µg/mL against the S. aureus ATCC 25923.	[16]
Fucus spiralis
Maceration RT, 4 days MeOH	Penicillium digitatum, Botrytis cinerea	Algae harvest in summer was active against both fungal species	[15]
Maceration RT: overnigth DCM:MeOH (1:1) PE EtAc n-Hx	Staphylococcus aureus, Bacillus subtilis, Bacillus cereus, Escherichia coli, Proteus mirabilis, Mucor mucedo, Trichophyton mentagrophytes, Aspergilus niger. Candida albicans, Penicillium italicum	The crude extract and fractions were active against all tested microbes; the best result was obtained with the lipidic fraction	[17]
Maceration 50°C, 24 h EtOH, AcO, EtAc, Chl and Hx, alga 0.03 g per mL of solvent	Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Pseudomonas aeruginosa. Salmonella enteritidis Escherichia coli	Acetonic extract was the most active	[11]
Sequential extraction Hx; EtAc, EtOH/Maceration EtOH, W/Shoxleth EtOH (frations W, Dieth, EtAc)	Staphylococcus epidermidis, Cutibacterium acnes, Malassezia furfur	The concentration used (1 mg/mL) is not effective against the studied microorganisms	[18]
Maceration AcO:W (7:3) and purification to obtain phlorotannins	Epidermophyton floccosum, Trichophyton rubrum, Trichophyton mentagrophytes, Microsporum canis and Microsporum gypseum	MIC values raking from 7.8 to 31.3 mg/mL against skin- and nail-isolated fungus	[19]
Sequential extraction MeOH, DCM/MeOH (50:50)/ DCM	Escherichia coli, Proteus mirabilis, Staphylococcus aureus CECT 976, Staphylococcus aureus, ATCC 25923	MIC of 3.6 µg/mL against P. mirabilis, 2.7 µg/mL against S. aureus CECT 976, and 10.65 µg/mL against the S. aureus ATCC 25923	[16]
Ascophyllum nodosum
Maceration RT 30 min MeOH:W (1:1)	Escherichia coli	Ascophyllum nodosum revealed antioxidant and antimicrobial capacity	[20]
Shoxleth ACO 6 h	Escherichia coli	Antimicrobial effect against E. coli in the first 6 h	[21]
Maceration AcO:W (7:3) 3 h RT and purification solid-phase extraction (SPE)	Escherichia coli, O157:H7 Salmonella agonaStreptococcus. suis	Mics of raking from 0.78 to 1.56 mg/mL	[6]
Maceration 50 °C, 24 h EtOH, AcO, EtAc, Chl and Hex	Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Pseudomonas aeruginosa, Salmonella enteritidis, Escherichia coli	The ethanolic extract was the most active	[11]

AcO: acetone, nBut: n-butanol, Chl: chloroform, cHx: cyclohexane, DCM: dichloromethane, Dieth: diethyl ether, EtOH: ethanol, EtAc: ethyl acetate, HX: hexane, IPr: isopropanol, MeOH: methanol, PE: petroleum ether, W: water, RT: room temperature.

Table 1. Selected studies on the antimicrobial activity of Bifurcaria bifurcata, Fucus spiralis, and Ascophyllum nodosum.

Extraction Technique	Microorganism Tested	Major Results	Ref.
Bifurcaria bifurcata
Sequential extraction (RT); (Hx, MeOH, Wt) 1:20 (m/v)	Epidermophyton floccosum, Microsporum canis, Microsporum gypseum, Trichophyton mentagrophytes var. interdigitale; Thrichophyton rubrum, Trichophyton verrucosum.	MeOH extracts demonstrated antifungal capacity against human dermatophyte fungi; the antifungal activity seems to be seasonally/geographically influenced	[14]
Maceration 50 °C, 24 h EtOH, AcO, EtAc, Chl and Hx	Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Pseudomonas aeruginosa, Salmonella enteritidis, Escherichia coli	Strong inhibition activity; all extracts were active against all microorganisms except E. coli	[11]
Maceration RT 60 min Hx–IPr-W (10:80:10)	Bacillus cereus; Bacillus subtilis; Geobacillus stearothermophilus; Listeria monocytogenes; Staphylococcus aureus; Staphylococcus haemolyticus;	MICs values between 0.9 mg/mL (B. cereus) and >19.9 (L. monocytogenes) spatial and seasonal variations; inconsistencies between disc diffusion and broth dilution methods	[12]
Maceration RT, 4 days MeOH	Penicillium digitatum, Botrytis cinerea	Active against both microorganisms in the four harvest seasons tested	[15]
Maceration 48 h, RT, +30 min. ultrasonication	Penicillium digitatum, Penicillium expansum, Penicillium italicum	Strong antifungal activity; effective in reducing the mycelial growth.	[13]
maceration RT 48 h methanol (90%)	E. coli, Staphylococcus aureus, Bacillo subtilis, P. aeruginosa	MICs from 0.11 to 1.87 mg/mL	[13]
Sequential extraction MeOH; DCM/MeOH (50:50), DCM	Escherichia coli, Proteus mirabilis, Staphylococcus aureus CECT 976, Staphylococcus aureus ATCC 25923	MIC of 0.02 µg/mL against P. mirabilis, 0.3 µg/mL against S. aureus CECT 976 and 1.8 µg/mL against the S. aureus ATCC 25923.	[16]
Fucus spiralis
Maceration RT, 4 days MeOH	Penicillium digitatum, Botrytis cinerea	Algae harvest in summer was active against both fungal species	[15]
Maceration RT: overnigth DCM:MeOH (1:1) PE EtAc n-Hx	Staphylococcus aureus, Bacillus subtilis, Bacillus cereus, Escherichia coli, Proteus mirabilis, Mucor mucedo, Trichophyton mentagrophytes, Aspergilus niger. Candida albicans, Penicillium italicum	The crude extract and fractions were active against all tested microbes; the best result was obtained with the lipidic fraction	[17]
Maceration 50°C, 24 h EtOH, AcO, EtAc, Chl and Hx, alga 0.03 g per mL of solvent	Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Pseudomonas aeruginosa. Salmonella enteritidis Escherichia coli	Acetonic extract was the most active	[11]
Sequential extraction Hx; EtAc, EtOH/Maceration EtOH, W/Shoxleth EtOH (frations W, Dieth, EtAc)	Staphylococcus epidermidis, Cutibacterium acnes, Malassezia furfur	The concentration used (1 mg/mL) is not effective against the studied microorganisms	[18]
Maceration AcO:W (7:3) and purification to obtain phlorotannins	Epidermophyton floccosum, Trichophyton rubrum, Trichophyton mentagrophytes, Microsporum canis and Microsporum gypseum	MIC values raking from 7.8 to 31.3 mg/mL against skin- and nail-isolated fungus	[19]
Sequential extraction MeOH, DCM/MeOH (50:50)/ DCM	Escherichia coli, Proteus mirabilis, Staphylococcus aureus CECT 976, Staphylococcus aureus, ATCC 25923	MIC of 3.6 µg/mL against P. mirabilis, 2.7 µg/mL against S. aureus CECT 976, and 10.65 µg/mL against the S. aureus ATCC 25923	[16]
Ascophyllum nodosum
Maceration RT 30 min MeOH:W (1:1)	Escherichia coli	Ascophyllum nodosum revealed antioxidant and antimicrobial capacity	[20]
Shoxleth ACO 6 h	Escherichia coli	Antimicrobial effect against E. coli in the first 6 h	[21]
Maceration AcO:W (7:3) 3 h RT and purification solid-phase extraction (SPE)	Escherichia coli, O157:H7 Salmonella agonaStreptococcus. suis	Mics of raking from 0.78 to 1.56 mg/mL	[6]
Maceration 50 °C, 24 h EtOH, AcO, EtAc, Chl and Hex	Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Pseudomonas aeruginosa, Salmonella enteritidis, Escherichia coli	The ethanolic extract was the most active	[11]

AcO: acetone, nBut: n-butanol, Chl: chloroform, cHx: cyclohexane, DCM: dichloromethane, Dieth: diethyl ether, EtOH: ethanol, EtAc: ethyl acetate, HX: hexane, IPr: isopropanol, MeOH: methanol, PE: petroleum ether, W: water, RT: room temperature.

This antifungal activity was also confirmed by studies conducted with methanolic extracts against P. digitatum and Botrytis cinerea [15]. In another study [14], the activity of methanolic extract was used in interrupting the growth of dermatophytic fungi. The authors concluded that the algal alga has an important inhibitory activity for the action on Epidermophyton floccosum and is one of the most effective algae in the published literature. In addition, the preservative effect of B. bifurcata extracts was tested on the quality of chilled hake quality shake. The results highlight the antimicrobial effect of aqueous and ethanolic B. bifurcata extracts in the icing media and demonstrate the potential of macroalgae bioactive compounds to preserve food quality [9].

Similarly, extracts of Fucus spiralis have been tested as antimicrobial and antifungal agents. A study on the antifungal activity of the methanolic extract of F. Spiralis against P. digitatum and Botrytis cinerea [15] showed a moderate effect but pointed out the seasonal variation of this property, since only the extracts from the alga harvested in summer were active. Inhibition of various Gram-positive and Gram-negative microorganisms has been described by N. Grozdanic et al. The most active antibacterial effect was achieved by the n-butanol fraction, with Mics values ranging from 0.04 mg/mL for B. cereus and B. subtilis to 0.14 mg/mL for P. mirabilis and E. coli. In the same study, the effect on the fungi Mucor mucedo, Trichophyton mentagrophytes, Aspergilus niger, C. albicans, and P. italicum was also investigated. In both cases (antimicrobial and antifungal activity), the lipid fraction was the most active [17]. This results agree with previous work stating the inhibition of several fungi by phlorotannis from F. spirailis [19]. The activity of F. spiralis extracts prepared by heat-assisted extraction with solvents of different polarity was assessed as solvent properties are an important factor in antimicrobial activity [22]. The results showed that the most active extract was obtained when acetone was used as a solvent, which was active against S. aureus, B. cereus, and Salmonella enteritidis [11]. The antimicrobial activity of F. spiralis extracts was also confirmed by results obtained with dichloromethane/methanol as an extracting solvent, which showed minimal inhibitory concentrations ranging from 2.7 ug/mL (S. aureus) to 1875 ug/mL (E. coli). Among other possibilities, F. spiralis extracts can be used for dermo-cosmetic applications, as they can contribute to the maintenance of a healthy skin microbiota [18].

The antimicrobial capacity of Ascophyllum nodosum was studied in vitro against E. coli serotype O138. The results show a dose-dependent relationship between the inhibitory activity and the concentration of the extract [20]; these results agree with those of Dell’Anno et al., who found an antibacterial action against E. coli O138 evidenced by a decrease in bacteria growth after 3 h attained by 0.12% Ascophyllum nodosum extract concentration, demonstrating a dose-dependent inhibitory effect [21].

The antimicrobial efficacy of an acetone–water mixture (7:3, v/v, 2 mL) A. nodosum extract purified phlorotannins against E. coli. O138, Salmonella agona, and Streptococcus suis have been examined before and showed a range of MICs for the different pathogens between 1.56 and 0.78 mg/mL. The authors also examined cell membrane permeability and intracellular adenosine triphosphate (ATP) to establish the inhibitory mechanism. They conclude that phlorotannin extracts dramatically lowered the intracellular ATP levels of all three microorganisms. Importantly, when subjected to the same or higher dosages that have been proven to inhibit bacterial growth (up to 25 mg/mL), the phlorotannin extracts exhibited no negative effects on pig intestinal cells, suggesting that they could be used as an alternative and supplement to antibiotics and zinc in animal diets [6].

In summary, we found that the three species of algae studied in this mini review have significant antimicrobial capacity, although it is worth pointing out that several factors affect their antimicrobial performance, from the extraction technique used to variations in maturation and provenience of the algal material. However, their applicability, e.g., as an aid in food preservation, is strong and is an interesting topic for future research into applied technology.